Early Mars Water Was Salty, Toxic Stew

As the recently landed Phoenix probe begins to unstow its robotic arm today, scientists are eagerly waiting for its analysis of Mars's arctic soil, which could offer new clues to the red planet's habitability.

But data from the rover Opportunity is already suggesting that water on early Mars billions of years ago may have been fit for pickling—not supporting—life.

"Liquid water is required by all species on Earth, and we've assumed that water is the very least that would be necessary for life on Mars," lead author Tosca said.

"However, to really assess Mars' habitability, we need to consider the properties of its water. Not all of Earth's waters are able to support life, and the limits of terrestrial life are sharply defined by water's temperature, acidity, and salinity."